Cell phone

From The IT Law Wiki

[edit] Overview

A cell phone (also called variously mobile phone, wireless phone, cellular telephone, cellphone, cell and hand phone) is a long-range, portable electronic device used for mobile communication that uses a network of specialized base stations known as cell sites. In addition to the standard voice function of a telephone, current cell phones can support many additional services, and accessories, such as SMS for text messaging, e-mail, packet switching for access to the Internet, and MMS for sending and receiving photos and video. Most current cell phones connect to a cellular network of base stations (cell sites), which is in turn interconnected to the public switched telephone network (PSTN) (the exception is satellite phones).

[edit] How cell phones work

When a cell phone is powered up, it acts as a scanning radio, searching through a list of control channels for the strongest signal. The cell phone re-scans every seven seconds or when the signal strength weakens, regardless of whether a call is placed. The cell phone searches for a five-digit number known as the System Identification Code assigned to service providers. After selecting a channel, the cell phone identifies itself by sending its programmed codes which identify the phone, the phone's owner, and the service provider. These codes include an Electronic Serial Number (a unique 32-bit number programmed into the phone by the manufacturer), and a Mobile Identification Number, a 10-digit number derived from the phone's number.

The cell site relays these codes to the mobile telecommunications switching office in a process known as registration. The registration process is explained in the Department of Justice's Electronic Surveillance Manual:

Cellular telephones that are powered on will automatically register or re-register with a cellular tower as the phone travels within the provider's service area. The registration process is the technical means by which the network identifies the subscriber, validates the account and determines where to route call traffic. This exchange occurs on a dedicated control channel that is clearly separate from that used for call content (i.e. audio) — which occurs on a separate dedicated channel. * * *

This registration process automatically occurs even while the cell phone is idle. Moving from one service area to another triggers the registration process anew. The cell site can even initiate registration on its own by sending a signal to the cell phone causing the phone to transmit and identify itself.^[1]

[edit] References

1. ↑ In re Application for Pen Register and Trap/Trace Device with In re Application for Pen Register and Trap/Trace Device with Cell Site Location Authority, 396 F.Supp.2d 747, 750-51 (S.D. Tex. 2005).

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